Methods for making a superconducting device with at least one enclosure

ABSTRACT

Some embodiments are directed to a device including multiple substrates comprising one or more troughs. The substrates are disposed such that the one or more troughs form at least one enclosure. At least one superconducting layer covers at least portion of the at least one enclosure. Other embodiments are directed to a method for manufacturing a superconducting device. The method includes acts of forming at least one trough in at least a first substrate; covering at least a portion of the first substrate with a superconducting material; covering at least a portion of a second substrate with the superconducting material; and bonding the first substrate and the second substrate to form at least one enclosure comprising the at least one trough and the superconducting material.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. application No. 61/754,298, filed Jan. 18, 2013, entitled, ERROR-CORRECTED QUANTUM REGISTERS FOR A MODULAR SUPERCONDUCTING QUANTUM COMPUTER, and U.S. application No. 61/871,061, filed Aug. 28, 2013, entitled, ERROR-CORRECTED QUANTUM REGISTERS FOR A MODULAR SUPERCONDUCTING QUANTUM COMPUTER, the entire contents of both are incorporated herein by reference.

FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant No. W911NF-09-1-0514 awarded by United States Army—Army Research Office. The US government has certain rights in the invention.

BACKGROUND

The present application relates generally to superconducting devices and methods of making superconducting devices. More specifically, the present application relates to superconducting devices formed from multiple substrates configured to exhibit quantum mechanical phenomena and methods for making such devices.

Quantum information processing uses quantum mechanical phenomena, such as energy quantization, superposition, and entanglement, to encode and process information in a way not utilized by conventional information processing. For example, it is known that certain computational problems may be solved more efficiently using quantum computation rather than conventional classical computation. However, to become a viable computational option, quantum computation requires the ability to precisely control a large number of quantum bits, known as “qubits,” and the interactions between these qubits. In particular, qubits should have long coherence times, be able to be individually manipulated, be able to interact with one or more other qubits to implement multi-qubit gates, be able to be initialized and measured efficiently, and be scalable to large numbers of qubits.

A qubit may be formed from any physical quantum mechanical system with at least two orthogonal states. The two states of the system used to encode information are referred to as the “computational basis.” For example, photon polarization, electron spin, and nuclear spin are two-level systems that may encode information and may therefore be used as a qubit for quantum information processing. Different physical implementations of qubits have different advantages and disadvantages. For example, photon polarization benefits from long coherence times and simple single qubit manipulation, but suffers from the inability to create simple multi-qubit gates.

Different types of superconducting qubits using Josephson junctions have been proposed, including “phase qubits,” where the computational basis is the quantized energy states of Cooper pairs in a Josephson Junction; “flux qubits,” where the computational basis is the direction of circulating current flow in a superconducting loop; and “charge qubits,” where the computational basis is the presence or absence of a Cooper pair on a superconducting island. Superconducting qubits are an advantageous choice of qubit because the coupling between two qubits is strong making two-qubit gates relatively simple to implement, and superconducting qubits are scalable because they are mesoscopic components that may be formed using conventional electronic circuitry techniques.

SUMMARY

The inventors have recognized and appreciated that superconducting devices may be manufactured using conventional microelectronic fabrication techniques. Accordingly, embodiments are directed to superconducting devices and methods for manufacturing superconducting devices.

Some embodiments are directed to a device including multiple substrates comprising one or more troughs. The substrates are disposed such that the one or more troughs form at least one enclosure. At least one superconducting layer covers at least a portion of the at least one enclosure. In some embodiments, the plurality of substrates comprise a material with a crystalline structure, such as silicon.

In some embodiments, the at least one enclosure is configured to form at least one three-dimensional cavity resonator such that electromagnetic radiation at one or more frequencies resonates within the at least one three-dimensional cavity resonator. The one or more frequencies may include at least one microwave frequency. A Q factor of the at least one three-dimensional cavity resonator may be greater than ten million. In some embodiments, the at least one three-dimensional cavity resonator comprises a first three-dimensional cavity resonator and a second three-dimensional cavity resonator. A Q factor of the first three-dimensional cavity resonator may be greater than a Q factor of the second three-dimensional cavity resonator.

In some embodiments, at least one superconducting qubit is coupled to the at least one three-dimensional cavity resonator. The at least one superconducting qubit may be a transmon qubit or a fluxonium qubit. In some embodiments, a superconducting wiring layer is disposed on and/or in a first substrate of the plurality of substrates. The superconducting wiring layer may be configured to couple the at least one superconducting qubit to the at least one three-dimensional cavity resonator. In some embodiments, at least one aperture in the at least one superconducting is configured to couple the superconducting wiring layer to the at least one three-dimensional cavity resonator. At least one via may connect the superconducting wiring layer to at least one superconducting component of a second substrate of the plurality of substrates.

In some embodiments, the at least one superconducting qubit is disposed within the at least one three-dimensional cavity resonator such that the at least one superconducting qubit is configured to couple to the at least one three-dimensional cavity resonator via electromagnetic radiation.

In some embodiments, the plurality of substrates of the device include a first substrate and a second substrate. The first substrate may include a first trough of the one or more troughs. The at least one superconducting layer may include a first superconducting layer that covers at least a portion of the first trough; and a second superconducting layer that covers at least a portion of a surface of the second substrate. The first substrate and the second substrate may be disposed such that the first superconducting layer and the second superconducting layer are in direct contact and the first trough forms the at least one three-dimensional cavity resonator.

In some embodiments, the at least one enclosure is configured to form at least one electromagnetic shield such that external electromagnetic radiation is prevented from entering the at least one enclosure. At least one superconducting component may be disposed within the at least one electromagnetic shield. The at least one superconducting component may include at least one superconducting circuit, at least one qubit and/or at least on stripline resonator.

In some embodiments, the plurality of substrates comprises a first substrate and a second substrate. The first substrate may include a first trough of the one or more troughs and the second substrate may include a second trough of the one or more troughs. The at least one superconducting layer may include a first superconducting layer that covers at least a portion of the first trough and a second superconducting layer that covers at least a portion of the second trough. The first substrate and the second substrate may be disposed such that the first trough and the second trough form the at least one enclosure. The at least one stripline resonator may be disposed within the at least one electromagnetic shield. In some embodiments, at least one support layer suspended within the at least one electromagnetic shield, wherein the at least one stripline resonator is disposed on and/or in the at least one support layer. The at least one support layer may include at least one material selected from the group consisting of silicon, silicon oxide, and silicon nitride. In some embodiments, the at least one electromagnetic shield is configure to be a part of a circuit associated with the at least one stripline resonator.

In some embodiments, the one or more troughs comprises a first trough with a first trough surface opposed to a second trough surface, wherein the first trough surface is not parallel to the second trough surface. The at least one surface of the one or more troughs may be atomically smooth. The at least one enclosure may evacuated to a pressure less than atmospheric pressure.

Some embodiments are directed to a method for manufacturing a superconducting device. The method includes acts of forming at least one trough in at least a first substrate; covering at least a portion of the first substrate with a superconducting material; covering at least a portion of a second substrate with the superconducting material; and bonding the first substrate and the second substrate to form at least one enclosure comprising the at least one trough and the superconducting material.

In some embodiments, the act of forming the at least one trough includes acts of: forming a mask layer that covers a portion of the first substrate; and etching a portion of the first substrate not covered by the mask layer. The act of etching may include an act of anisotropic etching using, for example, a wet etchant. The mask layer may include silicon nitride.

In some embodiments, the act of covering at least a portion of the first substrate with a superconducting material includes acts of: forming a seed layer on at least the portion of the first substrate; and electroplating the superconducting material onto the seed layer. The superconducting material may include one or more of aluminum, niobium, indium, rhenium, tantalum, titanium nitride, and niobium nitride.

In some embodiments, the method further includes acts of: forming channels in at least one wiring layer substrate; covering at least a portion of the channels with the superconducting material to form a wiring layer; and bonding the at least one wiring substrate to the first substrate and/or the second substrate. The act of forming at least one trough in at least a first substrate may include: forming a first trough in the first substrate; and forming a second trough in the second substrate, wherein the at least one enclosure comprises a first enclosure formed from the first trough and the second trough. In some embodiments, the at least one enclosure is configured to form at least one electromagnetic shield such that external electromagnetic radiation is prevented from entering the at least one enclosure. At least one superconducting component may be formed within the first enclosure. The at least one superconducting component may include at least one superconducting circuit, at least one qubit and/or at least one stripline resonator. In some embodiments, at least a portion of said second substrate is covered with a support layer and at least one qubit is disposed on and/or within the support layer within the cavity.

In some embodiments, the act of forming at least one trough in at least a first substrate further comprises forming a third trough in a third substrate, the method further comprising: covering at least a portion of the third substrate with the superconducting material; covering at least a portion of a fourth substrate with the superconducting material; bonding the third substrate and the fourth substrate to form a memory layer comprising a second enclosure from the third trough; and bonding the memory layer to the at least one wiring layer. The wiring layer may couple the second enclosure to the first enclosure. The first enclosure may be electrically connected to the wiring layer through at least one via. In some embodiments, a Q factor of the second enclosure is greater than a Q factor of the first enclosure.

In some embodiments, the method may also include coupling at least one qubit to the at least one enclosure. Coupling the at least one qubit to the at least one enclosure may include forming the at least one qubit within the at least one enclosure and/or forming the at least one qubit within the at least one enclosure. The at least one qubit may be a transmon qubit or a fluxonium qubit.

In some embodiments, the at least one enclosure is configured to form at least one three-dimensional cavity resonator such that electromagnetic radiation at one or more frequencies resonates within the at least one three-dimensional cavity resonator.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 illustrates a cross-sectional view of a superconducting device comprising a plurality of substrates and superconducting layers disposed to form a plurality of enclosures according to some embodiments;

FIG. 2 illustrates a cross-sectional view of a superconducting device comprising a three-dimensional cavity resonator enclosing a plurality of superconducting qubits disposed within the cavity according to some embodiments;

FIG. 3 illustrates a cross-sectional view of a superconducting device comprising an electromagnetic shield and a stripline resonator including a plurality of qubits according to some embodiments;

FIG. 4 illustrates a top view of a superconducting device comprising a stripline resonator comprising a plurality of superconducting qubits contained within an electromagnetic shield according to some embodiments;

FIG. 5 illustrates a cross-sectional view of a plurality of acts of a method for constructing a superconducting device according to some embodiments;

FIG. 6 illustrates a cross-sectional view of forming a trough in a substrate according to some embodiments;

FIG. 7 is a flowchart of a method for constructing a superconducting device according to some embodiments;

FIG. 8 is a flowchart of a method for forming a trough in a substrate according to some embodiments;

FIG. 9 is a method for constructing a superconducting device according to some embodiments; and

FIG. 10 is a method for constructing a superconducting device according to some embodiments.

DETAILED DESCRIPTION

The inventors have recognized and appreciated that the coherence times of superconducting devices can be significantly increased by using microelectronic fabrication techniques to form three-dimensional cavity resonators. These devices are less-sensitive to materials imperfections of both insulating substrates and conductors than more conventional, planar circuits. Significantly improved coherence times have been observed with three-dimensional resonators fabricated by conventional means. Such three-dimensional resonators may also benefit, in some embodiments, from having highly smoothed surfaces with few imperfections, that can result from etching techniques. In some embodiments, a three-dimensional cavity resonator may be used as a long-lived memory for quantum information. A superconducting qubit may be coupled to the three-dimensional cavity resonator such that quantum information transferred from the superconducting qubit to the photonic energy states of the three-dimensional cavity resonator. In some embodiments, one or more superconducting qubits may be coupled to a three-dimensional cavity resonator through a wiring layer. In other embodiments, one or more superconducting qubits may be disposed within the three-dimensional cavity resonator such that electromagnetic radiation within the cavity couples directly to the one or more superconducting qubits.

The inventors have recognized and appreciated that an enclosure formed from a superconducting material may shield components within the cavity from external electromagnetic noise, and prevent decoherence by suppressing losses due to electromagnetic radiation by the quantum circuit, even when the thickness of the superconducting material is small. Thus, superconducting layers may be formed to cover substrate layers to create precise, easily scaled superconducting devices. In some embodiments, an electromagnetic shield may enclose one or more superconducting qubits to shield the qubits from external noise, thereby increasing the performance of the superconducting qubits. For example, a stripline resonator comprising a plurality of superconducting qubits that act as a quantum bus may be disposed within an electromagnetic shield enclosure. Moreover, thin superconducting shields constructed between the parts or subunits of a large quantum processor will improve performance, reliability, and ease of calibration of the quantum device. In some embodiments, the quantum bus may be coupled to one or more other superconducting components such that quantum information from a first component may be transferred to a second component.

The inventors have also recognized and appreciated that using microelectronic fabrication techniques to manufacture superconducting devices comprising at least one superconducting enclosure for use in quantum information processing allows scalability that is not available when cavities are formed from bulk material. In some embodiments, a plurality of enclosures and superconducting qubits may be formed in a single device by forming troughs in a plurality of substrates and bonding the substrates together. In some embodiments, one or more wiring layers may be used to connect components together and or connect components to external devices. In some embodiments, one or more vias may interconnect components and/or wiring layers that are in different substrate layers. In this way, a plurality of superconducting qubits and/or enclosures may be interconnected in a compact space.

Microelectronic fabrication techniques are processes used in the manufacture of, for example, micrometer sized structures for semiconductor devices and/or microelectromechanical systems (MEMS). Examples of microelectronic fabrication techniques include, but are not limited to: deposition techniques, such as chemical vapor deposition (CVD) and physical vapor deposition (PVD); photolithography; etching techniques, such as dry etching, wet etching, reactive ion etching (RIE), isotropic etching and anisotropic etching; chemical-mechanical planarization; ion implantation techniques; and thermal oxidation techniques.

Throughout the present application, the term “enclosure” is used to describe a combination of superconducting layers that define a region of space that may be empty space or contain one or more superconducting devices of various types such as wiring, qubits, resonators, cavities, or other active devices within one or more substrates. A “three-dimensional cavity resonator” is a type of enclosure that is configured to support resonant electromagnetic radiation. An “electromagnetic shield” is a type of enclosure that is configured to prevent external electromagnetic radiation from entering the enclosure and prevent internal electromagnetic radiation from leaking out of the enclosure to the external environment.

FIG. 1 illustrates a superconducting device 100 according to one embodiment. The superconducting device comprises a plurality of substrates 101-105 that are bonded together in any suitable way. For example, two substrates that have been covered, at least partially, with a metal material may be bonded together using cold welding, thermocompression bonding, thermosonic bonding, eutectic bonding or solder reflow. Any suitable number of substrates may be bonded together to form superconducting device 100. The embodiment illustrated in FIG. 1 shows five separate substrates 101-105, but embodiments are not so limited. For example, some embodiments may bond only two substrates together.

The different substrates of the superconducting device 100 may serve different purposes. For example, substrate 101 and substrate 102 together form a bus layer, which is described in more detail in connection with FIGS. 3-4 below. Substrate 104 and substrate 105 together form a cavity memory layer, which is described in more detail below in connection with FIG. 2. Substrate 103 is used as an interconnection layer used to interconnect various components within the superconducting device 100. The interconnection layer comprises at least one wiring layer formed from a superconducting material disposed on and/or within the substrate 103 in a pattern that is configured to interconnect different components of the superconducting device 100.

The substrates 101-105 may comprise any suitable material. By way of example and not limitation, the material may include any material with a crystalline structure. For example, silicon or germanium may be used. However, in some embodiments, the substrate material may be insignificant as what controls the behavior of the superconducting device is the superconducting material that coats various portions of the substrate and the troughs that are created within the substrate to form enclosures. Additionally, the substrates 101-105 may be of any suitable dimensions. By way of example and not limitation, the substrates 101-105 may have a thickness ranging from 300 μm to 500 μm.

The superconducting layers of the superconducting device 100 may be formed in any suitable way. In some embodiments, the surface of the substrate is covered with a superconducting material. In other embodiments, one or more channels and/or troughs may be formed in the substrate that are subsequently covered, at least in part, with a superconducting material. Any suitable thickness of superconducting layer may be used. In some embodiments, a superconducting layer of superconducting device 100 may have a thickness ranging from 1 μm to 10 μm. Additionally, any suitable superconducting material may be used. By way of example and not limitation, the superconducting material may include aluminum, niobium, indium, rhenium, tantalum, titanium nitride, and/or niobium nitride.

In some embodiments, superconducting device 100 may communicate to external components via a planar-to-coaxial transition component 150 or any other suitable electronic connection, as known is in the art.

FIG. 1 illustrates a single cross-section of the device showing three separate enclosures 110, 120 and 130. One of skill in the art would recognize that other cross-sections at different positions into and out of the plane of the figure may include additional enclosures that may be coupled to the enclosures 110, 120 and 130 through the wiring layer 140, the vias 142 and 144, and/or additional wiring layers and vias not illustrated. Additionally, the wiring on a given layer or vias between layers may be separately enclosed by additional superconducting layers (not shown) realized by the same, or different, methods. The idea that all electromagnetic signals should be carried on properly designed transmission line structures, such as striplines or coaxial lines, and that these may be realized by the embodiment of our method for realizing superconducting enclosures, should be clear to one skilled in the art.

As mentioned above, a cavity memory layer may be formed from substrate 104 and 105. A trough is formed in the substrate 105 and covered, at least in part, with a superconducting layer 132. At least a portion of substrate 104 is also covered in a superconducting layer 134. The trough may be any suitable shape or size. For example, the trough may extend from a surface of the substrate by about 300 μm. The substrates are then positioned such that when connected together, a three-dimensional cavity resonator 130 is formed. FIG. 2 illustrates an embodiment 200 of a cavity memory layer in more detail. The three-dimensional cavity resonator 130 includes at least a first surface 232 and a second surface 234 that are opposed to one another. In some embodiments, the two surfaces are parallel to one other. In other embodiments, the first surface 232 and the second surface 234 may both form a non-perpendicular angle with the superconducting layer 134 associated with substrate 104. In some embodiments, every surface of the three-dimensional cavity resonator 130 is covered, at least in part, with a superconducting material. In some embodiments, each surface of the three-dimensional cavity is covered in its entirety except for two apertures 236 and 238 formed in the superconducting layer 134. The apertures 236 and 238 may be used to couple electromagnetic radiation into the three-dimensional cavity resonator 130 from the wiring layer 140. Other methods of coupling to the cavity, which would be known by those skilled in the art, may also be employed.

The geometry of the three-dimensional cavity resonator 130 determines which frequencies of electromagnetic radiation will be resonant with the cavity. In some embodiments, the three-dimensional cavity resonator 130 may be configured to resonate at microwave frequencies. By way of example and not limitation, the three-dimensional cavity resonator 130 may be configured to resonate at at least one frequency ranging between 1 GHz and 20 GHz. As a further example, the three-dimensional cavity 130 may be configured to resonate at at least one frequency ranging between 5 GHz and 9 GHz.

In some embodiments, the superconducting device 200 may include one or more superconducting qubits 131 disposed within the three-dimensional cavity resonator 130. Any suitable superconducting qubit may be used. By way of example and not limitation, each of the superconducting qubits 131 may be a transmon qubit or a fluxonium qubit. Each of the superconducting qubits 131 may comprise a Josephson junction disposed between two superconducting portions that act as a dipole antenna. In some embodiments the superconducting qubits 131 are oriented vertically such that the axis of each superconducting qubit (as determined by the orientation of the dipole antenna) is perpendicular to the superconducting layer 134 used to form the apertures 236 and 238, and the qubits thereby couple to the electromagnetic fields of the resonant cavity.

In other embodiments, the three-dimensional cavity resonator 130 does not contain a superconducting qubit, but is instead coupled to a superconducting qubit through wiring layer 140. In this way, an external superconducting qubit (not shown) may transfer quantum information to the three-dimensional cavity resonator 130, which may act as a memory for the quantum information.

Quantum information may be stored in the three-dimensional cavity resonator 130 in any suitable way. For example, the energy eigenstates of the electromagnetic field may be used as the computational basis for encoding quantum information. Alternatively, different coherent states and/or superpositions of coherent state (sometimes called “cat states”) may be used as the computational basis. Embodiments are not limited to any particular technique for encoding the quantum information in the three-dimensional cavity resonator 130.

As mentioned above, substrate 101 and substrate 102 of FIG. 1 form a bus layer. The bus layer includes enclosure 110 and enclosure 120, which are configured to be electromagnetic shields. Electromagnetic shield 110 includes a plurality of qubits 116 formed on and/or in a support layer 118 that is suspended within the electromagnetic shield 110. Electromagnetic shield 110 includes a superconducting layer 112 and a superconducting layer 114 for enclosing the qubits 116, thereby shielding the qubits 116 from external electromagnetic noise and preventing unwanted electromagnetic radiation from entering the enclosure. The electromagnetic shield 110 also prevents electromagnetic radiation from within the enclosure from leaking to the external environment. Similarly, electromagnetic shield 120 includes a plurality of qubits 126 formed on and/or in a support layer 128 that is suspended within the cavity 120. Electromagnetic shield 120 includes a superconducting layer 122 and a superconducting layer 124 for enclosing the qubits 126, thereby shielding the qubits 126 from external electromagnetic noise and preventing unwanted electromagnetic radiation or cross-coupling to other elements of the device.

FIG. 3 illustrates a more detailed cross-sectional view 300 of electromagnetic shield 110 according to some embodiments. Substrate 102 includes a trough from which the electromagnetic shield 110 is formed. At least a portion of the trough is covered with a superconducting layer 114. The superconducting layer 114 may also cover portions of the substrate 102 that are part of the trough. A plurality of qubits 116 are formed in and/or on a support layer 118. In some embodiments, the support layer is a dielectric membrane suspended across the trough in substrate 102. Any suitable material may be used to form the support layer. By way of example and not limitation, the support layer may comprise silicon, silicon oxide, or silicon nitride. The plurality of qubits 116 may be any suitable superconducting qubit, such as a transmon qubit or a fluxonium qubit. Each individual qubit of the plurality of qubits 116 may be individually controlled and/or detected using feed lines 312, which are formed in and/or on the support layer 118. A stripline resonator 310 is disposed between a first plurality of qubits and a second plurality of qubits. In some embodiments, the stripline resonator 310 may be approximately 20 μm wide. The feed lines 312 and the stripline resonator 310 may be formed from any suitable superconducting material.

Substrate 101 also includes a trough that has approximately the same dimensions and the trough in substrate 102. At least a portion of the trough in substrate 101 is covered with a superconducting layer 112. Substrate 101 is disposed near substrate 102 such that a gap exists between feedline 312 and superconducting layer 112. In some embodiments, the gap may be approximately 10 μm. Substrate 101 and substrate 102 may be in contact with each other at a location away from electromagnetic shield 110 such that they may be bonded together. By enclosing the stripline resonator 310 and the plurality of qubits 116 in an electromagnetic shield, the enclosed components are isolated from external electromagnetic noise, and decoherence due to unwanted electromagnetic radiation and cross-couplings are prevented.

FIG. 4 illustrates a top view 400 of the support layer 118 and the components included thereon. The arrows indicating “A” illustrate a plane representing the location of the cross-section view 300 of FIG. 3. Membrane 118 includes a plurality of superconducting qubits 116. In some embodiments, each superconducting qubit is a superconducting qubit, such as a transmon qubit or a fluxonium qubit. FIG. 4 illustrates transmon qubits 116 comprising a Josephson junction 412 between a first superconducting portion 414 and a second superconducting portion 416. Each qubit 116 may be individually controlled and/or read-out using drive feed lines 314. A large portion of the surface of the support layer 118 is covered with a superconducting layer as the ground plane for the stripline resonator 430. The stripline resonator 430 is driven via feedlines 420. There is a gap between the feedlines 420 and the stripline resonator such that the two components are weakly, capacitively coupled. Optionally, there are a plurality of holes 410 in the support layer 118 to reduce the amount of dielectric present in the enclosure in which the support layer is disposed and increase the amount of vacuum present in the enclosure, which may increase performance.

Superconducting devices according to certain embodiments may be manufactured in any suitable way. For example, microelectronic fabrication techniques may be used. Alternatively, the substrates may be formed with troughs and channels as desired using three-dimensional printing techniques and the superconducting layers may be formed using, for example, electroplating techniques. Some embodiments may create enclosures by forming a trough in a single substrate, as illustrate in FIG. 2. Alternatively, or in addition, enclosures may be created by forming a first trough in a first substrate and a second trough in a second substrate and placing the two substrates together with the two troughs adjacent to one another. Methods for forming superconducting devices according to some embodiments are described below with reference to FIGS. 5-10.

FIG. 5 illustrates a cross-sectional view of a plurality of acts of a method for constructing a superconducting device according to some embodiments. A flowchart of the acts of the method 700 according to some embodiments is shown in FIG. 7. At act 702, a first trough is formed in a first substrate. The trough may be formed in any suitable way. In some embodiments, the substrate and trough may be printed using three-dimensional printing techniques. In other embodiments, microelectronic fabrication techniques may be used. Details of one such embodiment is now described in connection with FIG. 5, FIG. 6 and FIG. 8.

FIG. 5A illustrates a first substrate 500 being provided. Any suitable substrate may be used. In some embodiments, the substrate may be formed from a material with a crystalline structure. For example, the substrate may comprise silicon or germanium. The substrate 500 may be of any suitable thickness. In the illustrated embodiments, the substrate is approximately 500 μm thick.

At act 802, a silicon nitride layer 502 is deposited on a first surface of the substrate 500 (see FIG. 5B). While silicon nitride is used in the illustrative embodiment of FIG. 5, any suitable material that may act as a mask may be used.

At act 804, a photoresist layer 504 is deposited on top of the silicon nitride layer 502 (see FIG. 5C). The photoresist layer 504 is formed in a pattern based on the dimensions of the trough being formed in the substrate 500. Accordingly, the photoresist layer is absent from the region above where the trough will be formed in the substrate in the subsequent acts. By way of example and not limitation, the photoresist layer 504 may be formed such that an area of the silicon nitride layer 502 with dimensions 18 mm by 38 mm is left exposed.

At act 806, the exposed portion of the silico nitride layer 502 is removed (see FIG. 5D). This may be achieved in any suitable way. In some embodiments, the silicon nitride layer 502 is etched using an etchant that removes the silicon nitride layer, but does not remove the photoresist. For example, reactive ion etching (RIE) may be used to etch the silicon nitride layer. The act of RIE may use, for example, CHF₃/O₂ as an etchant. The photoresist layer 504 is then removed at act 808. The resulting structure is the substrate 500 partially covered with the silicon nitride layer 502 which will act as a mask for defining dimensions of the trough (see FIG. 5E).

At act 810, the exposed portion of the substrate 500 is etched to form a trough 506. Any suitable etching may be performed. In some embodiments, the substrate 500 may be etched such that opposing surfaces of the resulting trough 506 are parallel to one another. In the embodiment shown in FIG. 5F, the trough is etched using an anisotropic wet etch using 30% KOH at 85° C. The details of the anisotropic etch is shown in more detail in FIG. 6.

FIG. 6 illustrates the trough 506 resulting from an anisotropic wet etch. Because of the crystalline structure of the silicon substrate 500, the (100) plane 612 and the (111) 614 plane for a 54.7° angle as a result of the etching act. In some embodiments, the anisotropic wet etch results in surfaces 612 and 614 that are atomically smooth. Thus, when covered in a superconducting layer the surface of the resulting enclosure will be substantially free from defects. If the enclosure is configured for use as a three-dimensional cavity resonator, the smooth surfaces result in a high Q factor cavity.

At act 812, the silicon nitride layer is removed resulting in the substrate 500 including the trough 506 (see FIG. 5G). While FIG. 8 illustrated one embodiment of a method for creating a trough in a substrate, any suitable method may be used. For example, laser machining or three-dimensional printing may be used to form a substrate with a trough.

Returning to FIG. 7, after the trough is formed in a substrate at act 702 the method 700 continues at act 704, where at least a portion of the first substrate is covered with a superconducting material. In some embodiments, all the surfaces of the trough in the substrate may be covered. In other embodiments, only portions of the surfaces may be covered. In this way, for example, apertures may be formed. In some embodiments, portions of the substrate outside of the region associated with the trough may also be covered with a superconducting layer.

The superconducting layer may be formed in any suitable way. For example, FIGS. 5H-I illustrate one particular method for forming a superconducting layer that covers at least a portion of the substrate. FIG. 5H illustrates a thin seed layer 508 is deposited over the surface of the substrate 500. This may be done in any suitable way. In some embodiments, copper is deposited via evaporation techniques to form the seed layer 508. Any suitable thickness of seed layer may be used. For example, the seed layer 508 may be approximately 200 nm thick. While copper is used as an example material for the seed layer 508, any suitable material may be used.

FIG. 5I illustrates a superconducting layer 510 formed on the seed layer 508. This may be done in any suitable way. For example, a superconducting material may be electroplated onto the seed layer. The superconducting layer 510 may be formed with any suitable thickness. For example, the superconducting layer 510 may be approximately 10 μm thick. Any suitable superconducting material may be used. For example, the superconducting layer may comprise aluminum, niobium, indium, rhenium, tantalum, titanium nitride, or niobium nitride.

At act 706, a second trough is formed in a second substrate. The act of forming the second trough may be achieved using the same techniques described in connection with act 702, FIG. 5 and FIG. 8. However, the formation of the second trough is optional. An enclosure may be formed from a single trough in a first substrate without forming a second trough in a second substrate.

At act 708, at least a portion of the second substrate is covered with a superconducting material. This act may be achieved using the techniques described in connection with act 704. In embodiments where a second trough is formed in the second substrate, at least a portion of every surface of the trough may be covered with a superconducting layer. In some embodiments, a portion of the second substrate outside of the trough region may be at least partially covered with a superconducting layer.

At act 710, at least one superconducting qubit is formed on a support layer. In some embodiments, the support layer may be any suitable dielectric membrane. For example, the support layer may comprise silicon, silicon oxide, or silicon nitride. In some embodiments, act 710 may be omitted as superconducting devices may be formed without a superconducting qubit being enclosed in an enclosure.

At act 712, the first substrate and the second substrate are bonded together to form an enclosure. In embodiments where the first trough was formed in the first substrate and a second trough was formed in the second substrate, the two troughs are positioned adjacent to one another such that the enclosure is formed from both troughs together. In some embodiments where at least one superconducting qubit is to be enclosed by an enclosure, the support layer is suspended across the first trough prior to bonding the two substrates together. Accordingly, the at least one qubit in and/or on the support layer is disposed within the enclosure.

The method 700 may also include additional optional acts shown in FIG. 9 and FIG. 10. For example, the result of performing method 700 may be the formation of enclosure 110 in the bus layer of FIG. 1. FIG. 9 illustrates additional acts for forming the wiring layer 140 and the memory layer enclosure 130. FIG. 10 illustrates additional acts for forming the second enclosure 120 in the bus layer.

FIG. 9 illustrates additional acts 900 for forming the wiring layer and the memory layer. In some embodiments, the additional acts may be performed after the method 700. In other embodiments, the additional acts may be performed before the method 700 or simultaneously with method 700.

At act 902, at least one channel is formed in wiring layer substrate 103 (see FIG. 1). The at least one channel may be formed, for example, using the same process used to create the trough in act 702.

At act 904, at least a portion of the at least one channel is covered with superconducting material. This may be achieved using the same process used above in connection with act 704. In some embodiments, the channel may be completely filled with superconducting material. In other embodiments, the one or more of the surfaces of the at least one channel may be covered with the superconducting material.

At act 906, the wiring substrate 103 is bonded to substrate 102. The substrates may be bonded in any suitable way, as discussed above.

At act 908, a trough is formed in substrate 105 using, for example, the same process used to create the trough in act 702.

At act 910, at least a portion of substrate 105 is covered with a superconducting material. This may be achieved using the same process used above in connection with act 704. In some embodiments, each surface of the through is completely covered with superconducting material. The superconducting material is formed in a layer that may be any suitable thickness. In some embodiments, the superconducting layer may be approximately 1 μm thick. In other embodiments, the superconducting layer may be approximately 10 μm thick.

At act 912, at least a portion of substrate 104 is covered with a superconducting material. This may be achieved using the same process used above in connection with act 704. Certain portions of a surface of substrate 104 may be left exposed. For example, the area corresponding to apertures 236 and 238 in FIG. 2 may not be covered with superconducting material.

At act 914, substrate 104 is bonded to substrate 105 such that the trough forms a three-dimensional cavity resonator. The substrates may be bonded in any suitable way, as discussed above.

At act 916, the memory layer is bonded to the wiring layer. The substrates associated with the layers may be bonded in any suitable way, as discussed above.

FIG. 10 illustrates additional acts for forming the second enclosure 120 in the bus layer.

At act 1002, a trough associated with enclosure 120 is formed in the substrate 101 using, for example, the same process used to create the trough in act 702. In some embodiments, the trough associate with enclosure 120 may be formed simultaneously with the trough associated with enclosure 110.

At act 1004, a trough associated with enclosure 120 is formed in the substrate 102 using, for example, the same process used to create the trough in act 702. In some embodiments, the trough associate with enclosure 120 may be formed simultaneously with the trough associated with enclosure 110.

At act 1006, at least a portion of substrate 102 may be covered with a support layer which is suspended over the trough associated with enclosure 120. This support layer may be formed in the same way as the support layer associated with enclosure 110.

At act 1008, at least one qubit is formed on the support layer. This at least one qubit may be formed in the same way as the support layer associated with enclosure 110.

Having thus described several aspects of at least one embodiment of a superconducting device and at least one method for manufacturing a superconducting device, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. For example, superconducting enclosures of any size may be included. Some enclosures may have dimensions on the order of a centimeter, a millimeter, or a micrometer. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. While the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.

While various inventive embodiments have been described and illustrated, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure may be directed to each individual feature, system, system upgrade, and/or method described. In addition, any combination of two or more such features, systems, and/or methods, if such features, systems, system upgrade, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

Further, though some advantages of the described embodiments may be indicated, it should be appreciated that not every embodiment will include every described advantage. Some embodiments may not implement any features described as advantageous. Accordingly, the foregoing description and drawings are by way of example only.

The section headings used are for organizational purposes only and are not to be construed as limiting the subject matter described in any way.

Also, the technology described may be embodied as a method, of which at least one example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. In addition, certain acts performed as part of the method may be optional. Accordingly, embodiments may be constructed in which certain acts are not performed at all.

All definitions, as defined and used, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The terms “about,” “approximately,” and “substantially” may be used to refer to a value, and are intended to encompass the referenced value plus and minus acceptable variations. The amount of variation could be less than 5% in some embodiments, less than 10% in some embodiments, and yet less than 20% in some embodiments. In embodiments where an apparatus may function properly over a large range of values, e.g., a range including one or more orders of magnitude, the amount of variation could be a factor of two. For example, if an apparatus functions properly for a value ranging from 20 to 350, “approximately 80” may encompass values between 40 and 160.

The indefinite articles “a” and “an,” as used in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

The phrase “and/or,” as used in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively.

The claims should not be read as limited to the described order or elements unless stated to that effect. It should be understood that various changes in form and detail may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. All embodiments that come within the spirit and scope of the following claims and equivalents thereto are claimed.

Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. 

What is claimed is:
 1. A method for manufacturing a superconducting device, the method comprising acts of: forming at least one trough in at least a first substrate; covering at least a portion of the first substrate with a superconducting material; covering at least a portion of a second substrate with the superconducting material; and bonding the first substrate and the second substrate to form at least one enclosure comprising the at least one trough and the superconducting material.
 2. The method of claim 1, wherein the act of forming the at least one trough comprises acts of: forming a mask layer that covers a portion of the first substrate; and etching a portion of the first substrate not covered by the mask layer.
 3. The method of claim 2, wherein the act of etching comprises an act of anisotropic etching.
 4. The method of claim 3, wherein the act of anisotropic etching uses a wet etchant.
 5. The method of claim 2, wherein the mask layer comprises silicon nitride.
 6. The method of claim 1, wherein the act of covering at least a portion of the first substrate with a superconducting material comprises acts of: forming a seed layer on at least the portion of the first substrate; and electroplating the superconducting material onto the seed layer.
 7. The method of claim 1, wherein the superconducting material is selected from the group consisting of aluminum, niobium, indium, rhenium, tantalum, titanium nitride, and niobium nitride.
 8. The method of claim 1, further comprising: forming channels in at least one wiring layer substrate; covering at least a portion of the channels with the superconducting material to form a wiring layer; and bonding the at least one wiring substrate to the first substrate and/or the second substrate.
 9. The method of claim 8, wherein the act of forming at least one trough in at least a first substrate comprises: forming a first trough in the first substrate; and forming a second trough in the second substrate, wherein the at least one enclosure comprises a first enclosure formed from the first trough and the second trough.
 10. The method of claim 9, wherein the at least one enclosure is configured to form at least one electromagnetic shield such that external electromagnetic radiation is prevented from entering the at least one enclosure.
 11. The method of claim 10, further comprising: forming at least one superconducting component within the first enclosure.
 12. The method of claim 11, wherein the at least one superconducting component comprises at least one superconducting circuit.
 13. The method of claim 11, wherein the at least one superconducting component comprises at least one qubit.
 14. The method of claim 13, further comprising: covering at least a portion of said second substrate with a support layer, wherein the at least one qubit is disposed on and/or within the support layer.
 15. The method of claim 13, wherein the at least one superconducting component comprises at least one stripline resonator.
 16. The method of claim 15, wherein the act of forming at least one trough in at least a first substrate further comprises forming a third trough in a third substrate, the method further comprising: covering at least a portion of the third substrate with the superconducting material; covering at least a portion of a fourth substrate with the superconducting material; bonding the third substrate and the fourth substrate to form a memory layer comprising a second enclosure from the third trough; and bonding the memory layer to the at least one wiring layer.
 17. The method of claim 16, wherein: the wiring layer couples the second enclosure to the first enclosure.
 18. The method of claim 17, wherein: the first enclosure is electrically connected to the wiring layer through at least one via.
 19. The method of claim 16, wherein: a Q factor of the second enclosure is greater than a Q factor of the first enclosure.
 20. The method of claim 1, further comprising: coupling at least one qubit to the at least one enclosure.
 21. The method of claim 20, wherein coupling the at least one qubit to the at least one enclosure comprises forming the at least one qubit within the at least one enclosure.
 22. The method of claim 20, wherein coupling the at least one qubit to the at least one enclosure comprises forming the at least one qubit within the at least one enclosure.
 23. The method of claim 20, wherein the at least one qubit is a transmon qubit.
 24. The method of claim 20, wherein the at least one qubit is a fluxonium qubit.
 25. The method of claim 1, wherein the at least one enclosure is configured to form at least one three-dimensional cavity resonator such that electromagnetic radiation at one or more frequencies resonates within the at least one three-dimensional cavity resonator.
 26. The method of claim 1, wherein the at least one enclosure is configured to form at least one three-dimensional cavity resonator such that electromagnetic radiation at one or more frequencies resonates within the at least one three-dimensional cavity resonator. 